The long term objective of the project is to provide chemical and physical information about the root caries process which will help with a better understanding of the mechanisms involved. This work will aid the development of more efficient preventive measures, and in particular will add to the understanding of the role of flouride in root caries prevention or reversal. The prevention and treatment of root caries is rapidly becoming an area of major importance in dentistry. Little is known of its histology, chemical mechanisms, or the effect of fluoride on root caries. The present proposal is designed to provide information from in vitro experiments which will answer some of the many questions about the effective management of root caries. The specific aims are: (1) to study extracted teeth containing natural carious lesions of the root. The techniques to be used are optical microscopy, qualitative polarized light microscopy, and microhardness profiles, (2) to develop chemical artificial caries systems which produce root caries in vitro with similar histological characteristics to natural root caries, (3) to measure the rate of lesion progress in vitro in the chemical model systems, by the use of chemical analysis as well as physical means, (4) to assess the inhibitory effect of flouride on the rate of lesion progress when flouride is present during te acid challenge (5) to study the potential of a range of proprietary flouride preparations to enhance remineralization during cyclic de- and re- mineralization of roots in vitro. Experimental remineralizing solutions will be tested similarly, (6) to bring this information together to provide a preliminary mechanistic understanding of the chemical and physical processes involved in root caries and the role of flouride in these processes. Caries of the tooth root appears to be a major problem in the elderly. However, the true extent of the problem is unknown. Neither the etiology nor histology are currently understood. Satisfactory preventive methods have yet to be developed. The studies of the present project will give some understanding of the physico-chemical mechanisms involved in root caries. They will illustrate some aspects of the role of various flouride regimes in prevention, and together with the studies of other workers should lead to improved clinical management of root caries.